Avian infectious bronchitis is an acute and contagious disease which affects poultry mainly through respiratory symptoms. The avian infectious bronchitis virus (or IBV) is a member of the Coronavirus genus, family Coronaviridae, order Nidovirales. This single-stranded RNA virus has a strong capacity for evolution, and the viral particles can survive for a period of one month in the outside environment. IBV affects poultry of all ages and does not target only the respiratory tracts. Indeed, IBV replicates first of all in the trachea and can subsequently spread throughout the body of the affected fowl, affecting various internal organs.
Morbidity is high and mortality can vary according to farms, to farming conditions and also to sites of bacterial superinfections.
The clinical signs are of the following types:                respiratory (coughing, tracheal rales, swollen sinuses, conjunctivitis, etc.);        reproductive (decrease in egglaying, production of eggs with thin, deformed or colored shells);        renal, intense thirst, etc.        
IBV is transmitted especially by the respiratory pathway, or via aerosols. The virulent materials are made up of nasal discharge and droppings. Transmission is horizontal, directly (from sick birds to sensitive birds), or indirectly (via water, material, etc.).
IBV is sensitive to most disinfectants, but the best means of containment consists of vaccination allied to taking biosafety steps (decontamination steps, disinfection steps, etc.).
Vaccination consists in inoculating the species to be protected with an amount of killed pathogen (inactivated vaccine) or pathogen of which the virulence has been reduced (live attenuated vaccine) in order to trigger a biological response in the host, protecting it during the subsequent occurrence of the disease.
Live vaccines are generally sufficiently effective so as not to require the use of adjuvants.
A vaccine adjuvant is an excipient which amplifies the biological response against the antigen with which it is combined. Mention will be made, for example, of aluminum hydroxide, and the oily adjuvants sold under the name Montanide™ by the company SEPPIC. These adjuvants are of various natures. They can just as well consist of liposomes, of emulsions comprising at least one oily phase and at least one aqueous phase, of the “Freund's” adjuvant type, or more commonly of water-insoluble inorganic salts. Among the inorganic salts used as vaccine composition adjuvants, mention may, for example, be made of aluminum hydroxide, cerium nitrate, zinc sulfate, colloidal iron hydroxide or calcium chloride. Aluminum hydroxide is the adjuvant most commonly used. These inorganic salts used as vaccine composition adjuvants are described in particular in the article by Rajesh K. Gupta et al., “Adjuvants, balance between toxicity and adjuvanticity”, Vaccine, vol. 11, Issue 3, 1993, pages 293-306.
Vaccines can be administered by injection (subcutaneous or intramuscular injection) or locally (mass vaccination by nebulization, addition to the drinking water for contact with the beak and nostrils and the oculonasal complex, for example). Vaccination by injection, even if it proves to be effective, has the drawback of not being suitable for the economic context of poultry farms (high labor cost), and it also causes stress in the poultry treated, which, in the case of egg-layers, can lead to disruptions in egglaying following the physical trauma caused by the injection.
The use of effective adjuvants in vaccine compositions, and in vaccine compositions intended for preventing the occurrence of infectious bronchitis, makes it possible:                to increase the strength of the protective response, making it possible to provide a better level of protection;        to prolong the duration of the protection conferred by a vaccine dose, providing longer-lasting protection of the animals in farms throughout their growth;        to provide sufficient protection with a single treatment when two treatments were necessary in the absence of these immune response amplifiers. The saving is then in the number of doses to be injected (halved), the handling of the animals (labor) and the stress caused during the handling of the animals (also halved);        to have the possibility of obtaining, with a lower antigenic dose, an efficacy equivalent to that conferred by a complete dose used without adjuvant. Thus, the vaccine production plant will, with the same productive capacity, be capable of producing a higher number of vaccine doses. Likewise, an existing packaging may be proposed for vaccinating a larger number of animals.        
No adjuvant is described or used at the current time during the implementing of vaccination techniques by local administration using live vaccines.
There is a need to develop diluents which also have the adjuvant function for improving the immune response as described above. These compositions are referred to as adjuvant diluents (ADs).
The main difficulty encountered in the development of an AD is the ability of said adjuvant diluent (AD) to keep the live vaccine alive so that it retains its immunogenic properties.
An important element of the development of adjuvants for live vaccines lies in the specificity of the adjuvant formulations for not killing the live microorganisms constituting the vaccine antigens when they are brought into contact before injection. ADs exist on the market (such as, for example, tocopheryl acetate from the company Intervet included in Diluvac Forte®) and are recommended for certain live vaccines.
Furthermore, a live vaccine is known in French patent application FR 2 385 401.
However, this live vaccine is not prepared with adjuvant substances. It has up until now been taken as read that the greater immune response could be produced with a live vaccine, for example, by increasing the content of virus, or by using a more immunogenic strain.